Here’s a great low cost filament extruder solution. It uses basic parts available from any hardware store, and a few 3D printed ones — estimated cost is well under $100.
It’s very similar to the Lyman Filament Extruder, but can be built for even less money. By using 200C set-point heaters, his setup requires absolutely no electronics — although a cheap PID controller from China could give him more extrusion capabilities with temperature control… Regardless, the system appears to make good filament and he uses it exclusively for his personal filament consumption in his Delta printer. He’s even hacked up the ABS casing of a refrigerator, ground it down, and turned it into filament using this machine! If you’re hungry for more details, the full build log and discussion can be found on the RepRap forums.
He also has a guide on making your own ABS color masterbatch to make your own filament colors!